Conventionally, when manufacturing a semiconductor component, a flat panel display, or the like, various liquid processings such as cleaning or etching are performed on a substrate such as a semiconductor wafer or a liquid crystal substrate by using a substrate processing apparatus.
For example, in a substrate processing apparatus configured to perform cleaning of a substrate, a chemical liquid for cleaning is supplied to the substrate which is being rotated, and a surface of the substrate is cleaned with the chemical liquid. Then, a rinse liquid is supplied to a central portion of the substrate, and the surface of the substrate is rinsed with the rinse liquid. In this rinsing process, by supplying a processing liquid (e.g., pure water) for rinsing the surface of the substrate to the substrate, a liquid film of the processing liquid is formed on the surface of the substrate. Thereafter, the supply of the processing liquid is stopped, and by supplying a drying solution (e.g., IPA (isopropyl alcohol)) having a higher volatility than the processing liquid to the central portion of the substrate, a replacement process of replacing the liquid film of the processing liquid formed on the surface of the substrate with the drying solution is performed. In this replacement process, a liquid film of the drying solution is formed on the surface of the substrate as the processing liquid is replaced by the drying solution, starting from the central portion of the substrate toward an outer peripheral side thereof. Afterwards, an inert gas (e.g., nitrogen gas) is discharged toward the drying solution, and by dispersing the drying solution outwards from the surface of the substrate with a centrifugal force which is generated as the substrate is rotated, the surface of the substrate is dried.
As stated, in the conventional substrate processing apparatus, when performing the drying of the substrate, the liquid film of the processing liquid is formed on the surface of the substrate by supplying the processing liquid thereto, and the supply of the drying solution is begun after the supply of the processing liquid is stopped. Accordingly, the liquid film of the processing liquid formed on the surface of the substrate is replaced by the drying solution (see, for example, Japanese Patent Laid-open Publication No. 2010-045389).
The centrifugal force generated by the rotation of the substrate is applied to the liquid film of the processing liquid which is formed on the surface of the substrate. This centrifugal force is stronger at an outer peripheral portion of the substrate than at the central portion thereof. Therefore, after the supply of the processing liquid is stopped and before the liquid film of the drying solution is formed on the entire surface of the substrate after the supply of the drying solution is begun, the liquid film of the processing liquid formed on the outer peripheral portion of the substrate may be shaken off outwards from the substrate, so that the liquid film may be cut at the outer peripheral portion of the substrate. This cutting of the liquid film may easily take place especially in a case where the surface of the substrate is hydrophobized.
That is, as depicted in a schematic diagram of FIG. 13, though the liquid film of the drying solution is formed without being cut at the central portion of the substrate (within a circular region concentric with the substrate, indicated by a dashed dotted line), the liquid film of the drying solution is cut at the outer peripheral portion of the substrate. As a result, a liquid droplet of the drying solution is formed at the outer peripheral portion of the substrate. If the liquid droplet is dried while a substance (e.g., ammonia) contained in the atmosphere is dissolved in the liquid droplet, a watermark or a particle may be generated on the surface of the substrate.
When supplying the replacement liquid, it may be considered to keep the liquid film of the processing liquid by reducing the centrifugal force by way of decreasing a rotational speed of the substrate. If so, however, a processing time is increased, so that a throughput of the substrate processing apparatus is reduced.